A drooping of the upper eyelid below its normal level resulting in narrowing of the palpebral opening is known in ophthalmology as ptosis. The muscle controlling lid opening is the levator palpebrae superioris and it is innervated by the third cranial nerve (oculomotor nerve). Ptosis may be congenital or acquired. In congenital ptosis the levator palpebrae superioris muscle that elevates the lid is either absent or not well developed. Acquired ptosis, on the other hand, is usually due to either diseases or injuries of the nerves that control the movements of the levator palpebrae superioris muscle. Ptosis may further be classified as myogenic, aponeurotic, neurogenic, mechanical or traumatic.
The treatment of ptosis has traditionally required accurate and consistent evaluation and measurement as well as skillful use of surgical techniques to implement a functional and aesthetic correction. In most cases, surgery has been required to correct a ptotic eyelid. The surgical procedures used generally depend on the severity of ptosis and are described in the following references, each of which is incorporated by reference in its entirety for all purposes: Callahan M, Beard C: Ptosis, 4th ed. Birmingham: Aesculapius, 1990; Dresner S. C.: Further modifications of the Müller's muscle conjunctival resection procedure. Ophthalmic Plast Reconstr Surg 1991; 7:114-122; Dresner S. C.: Minimal ptosis management. In: Kikkawa D. O., ed. Aesthetic Ophthalmic Plastic Surgery. Philadelphia: Lippincott-Raven, 1997:151-162; Older II: Ptosis repair and blepharoplasty in the adult. Ophthalmic Surg 1995; 4:304-308; and Crawford I. S.: Repair of ptosis using frontalis muscle and fascia lata: a 20 year review. Ophthalmic Surg 1977; 8:31-40.
The amount of levator function present generally determines which surgical procedure will be adopted. For minimal ptosis, Müllerectomy or Fasanella-Servat procedures have been used. Levator aponeurotic surgical repair has been used for patients with involutional changes. Frontalis suspension and Whitnall's sling have been used for more severe cases of ptosis.
In the frontalis suspension operation, the eyelid is suspended from the frontalis so that the eyelid is opened when the patient lifts the eyebrow using the frontalis muscle. Tendon tissue from the patient's leg or biocompatible synthetic materials are also used. While this procedure allows the patient to raise the eyebrow to open the eyelid and therefore see from the eye, it suffers from a number of drawbacks. The patient must adapt to the uncommon, tiring and uncomfortable movement of raising the eyebrow to raise the eyelid. Furthermore, the extent to which the patient is able to raise the eyelid varies from procedure to procedure. Essentially, the procedure restores some eyelid function but that function is not natural. This procedure is also a cosmetic failure because of the requirement for the patient to raise his or her eyebrow.
U.S. Pat. No. 5,522,889 to Baker et al. entitled “Apparatus and method for restoring eyelid function,” teaches an apparatus to restore eyelid function in a patient unable to voluntarily raise an eyelid. The apparatus includes a spiral torsion spring and pulley arrangement mounted in a housing that is implanted in fixed positions in the superior portion of the orbit of the eye. A wire connects the pulley to the eyelid. A spiral torsion spring provides the necessary spring force in tension to overcome the weight of the eyelid and draw the eyelid open. The natural muscles of eye closure are, however, sufficiently strong to overcome the spring tension thereby playing out wire from the pulley and closing the eye so as to provide normal blinking function. A position setting gear allows the biasing force of the spring to be selectively reduced sufficiently to allow the eye to remain closed for sleep or at other desired times.